U.S. patent application number 14/069096 was filed with the patent office on 2014-05-08 for condition estimation device and method of estimating condition.
This patent application is currently assigned to GS Yuasa International Ltd.. The applicant listed for this patent is GS Yuasa International Ltd.. Invention is credited to Masashi Nakamura, Kenichi Sejima.
Application Number | 20140125345 14/069096 |
Document ID | / |
Family ID | 49641474 |
Filed Date | 2014-05-08 |
United States Patent
Application |
20140125345 |
Kind Code |
A1 |
Sejima; Kenichi ; et
al. |
May 8, 2014 |
CONDITION ESTIMATION DEVICE AND METHOD OF ESTIMATING CONDITION
Abstract
A condition estimation device for estimating condition of an
electric storage device includes a voltage detector and a
controller. The voltage detector is configured to detect a voltage
of the electric storage device. The controller is configured to
perform a distinctive point detection process to detect a
distinctive point based on the voltage detected by the voltage
detector, and an estimation process to estimate the condition of
the electric storage device based on the distinctive point detected
in the distinctive point detection process. The distinctive point
is a point at which a variation in voltage per unit remaining
capacity or per unit time of the electric storage device during
charge or discharge is a local maximum value.
Inventors: |
Sejima; Kenichi; (Kyoto-shi,
JP) ; Nakamura; Masashi; (Kyoto-shi,, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GS Yuasa International Ltd. |
Kyoto-shi, |
|
JP |
|
|
Assignee: |
GS Yuasa International Ltd.
Kyoto-shi,
JP
|
Family ID: |
49641474 |
Appl. No.: |
14/069096 |
Filed: |
October 31, 2013 |
Current U.S.
Class: |
324/426 |
Current CPC
Class: |
G01R 31/3835 20190101;
G01R 31/367 20190101; G01R 31/392 20190101; G01R 31/396 20190101;
G01R 31/3648 20130101 |
Class at
Publication: |
324/426 |
International
Class: |
G01R 31/36 20060101
G01R031/36 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2012 |
JP |
2012-243668 |
Jan 31, 2013 |
JP |
2013-017152 |
May 14, 2013 |
JP |
2013-102179 |
Claims
1. A condition estimation device for estimating condition of an
electric storage device, the condition estimation device
comprising: a voltage detector configured to detect a voltage of
the electric storage device; a controller configured to perform: a
distinctive point detection process to detect a distinctive point
based on the voltage detected by the voltage detector, the
distinctive point being a point at which a variation in voltage per
unit remaining capacity or per unit time of the electric storage
device during charge or discharge is a local maximum value: and an
estimation process to estimate the condition of the electric
storage device based on the distinctive point detected in the
distinctive point detection process.
2. The condition estimation device according to claim 1, wherein
the controller is configured to perform the estimation process to
estimate the condition of the electric storage device based on the
voltage of the electric storage device at which the distinctive
point appears.
3. The condition estimation device according to claim 1, wherein
the controller is configured to perform the estimation process to
estimate a remaining capacity of the electric storage device based
on the distinctive point detected in the distinctive point
detection process.
4. The condition estimation device according to claim 1, wherein
the distinctive point includes a plurality of distinctive points,
and the controller is configured to select one of the distinctive
points in a higher voltage region in the distinctive point
detection process.
5. The condition estimation device according to claim 1, wherein
the controller is configured to: perform a period measurement
process to measure a period from when the distinctive point
detected in the distinctive point detection process appears until
when a voltage of the electric storage device reaches a set
voltage, and perform the estimation process to estimate the
condition of the electric storage device based on the period
measured in the period measurement process.
6. The condition estimation device according to claim 5, wherein
the controller is configured to detect whether the voltage of the
electric storage device reaches the set voltage based on the
voltage of the electric storage device detected by the voltage
detector.
7. The condition estimation device according to claim 5, wherein
the set voltage is a switching voltage at which a charge mode for
charging the electric storage device is switched.
8. The condition estimation device according to claim 1, wherein
the controller is configured to perform the distinctive point
detection process to determine the distinctive point based on the
variation in voltage per unit remaining capacity or per unit time
of the electric storage device during the charge.
9. The condition estimation device according to claim 1, wherein
the electric storage device includes a negative active material
including graphite.
10. The condition estimation device according to claim 1, wherein
the controller is configured to perform a deterioration estimating
process to estimate a deterioration level of the electric storage
device.
11. A condition estimation method for estimating condition of an
electric storage, the method comprising: detecting a distinctive
point based on a voltage of the electric storage device detected by
a voltage detector, the distinctive point being a point at which a
variation in voltage per unit remaining capacity or per unit time
of the electric storage device during charge or discharge is a
local maximum value; and estimating the condition of the electric
storage device based on the distinctive point.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from Japanese Patent
Applications No. 2012-243668 filed on Nov. 5, 2012, No. 2013-017152
filed on Jan. 31, 2013, and No. 2013-102179 filed on May 14, 2013.
The entire content of the priority applications is incorporated
herein by reference.
FIELD
[0002] The present invention relates to a technology for estimating
a condition of an electric storage device, and a method of
estimating a condition of an electric storage device.
BACKGROUND
[0003] Patent Document JP-A-2003-232839 discloses a technology for
determining a capacity of a secondary battery based on calculation
of a current accumulated from a predetermined fully discharged
condition to a predetermined fully charged condition.
[0004] However, it may be difficult to charge the electric storage
device in a predetermined fully discharged condition until the
electric storage device satisfies a fully charged condition
depending on how a device in which the electric storage device is
installed is used. The electric storage device may not be fully
charged until it satisfies a predetermined fully charged condition
or fully discharged until it satisfies a predetermined fully
discharged condition depending on how the device is used.
SUMMARY
[0005] The following presents a simplified summary of the invention
disclosed herein in order to provide a basic understanding of some
aspects of the invention. This summary is not an extensive overview
of the invention. It is intended to neither identify key or
critical elements of the invention nor delineate the scope of the
invention. Its sole purpose is to present some concepts of the
invention in a simplified form as a prelude to the more detailed
description that is presented later.
[0006] A technology disclosed herein is for estimating a condition
of an electric storage device, such as a capacity of the electric
storage device and an internal resistance, without discharging or
charging the electric storage device until the electric storage
device satisfies a predetermined fully charged condition or a
predetermined fully discharged condition.
[0007] A condition estimation device for estimating condition of an
electric storage device includes a voltage detector and a
controller. The voltage detector is configured to detect a voltage
of the electric storage device. The controller is configured to
perform a distinctive point detection process to detect a
distinctive point based on the voltage detected by the voltage
detector, and an estimation process to estimate the condition of
the electric storage device based on the distinctive point detected
in the distinctive point detection process. The distinctive point
is a point at which a variation in voltage per unit remaining
capacity or per unit time of the electric storage device during
charge or discharge is a local maximum value.
BRIEF DESCRIPTION OF DRAWINGS
[0008] The foregoing and other features of the present invention
will become apparent from the following description and drawings of
an illustrative embodiment of the invention in which:
[0009] FIG. 1 is a schematic view illustrating a configuration of a
battery pack according to an embodiment;
[0010] FIG. 2 is a schematic view illustrating a configuration of a
battery module;
[0011] FIG. 3 is a graph illustrating variations in voltage,
variations in voltage per unit remaining capacity or per unit time,
and variations in charge current of a secondary battery during
charge at an ambient temperature of 25.degree. C.;
[0012] FIG. 4 is a table including correlation data that represent
a correlation between a voltage V at which a second distinctive
point P2 appears and a battery capacity;
[0013] FIG. 5 is a graph illustrating variations in voltage,
variations in voltage per unit remaining capacity or per unit time,
and variations in charge current of a secondary battery during
discharge at an ambient temperature of 25.degree. C.;
[0014] FIG. 6 is a graph illustrating variations in voltage and
variations in voltage per unit remaining capacity or per unit time
of the secondary battery during charge at a charge rate of 0.2
(CA);
[0015] FIG. 7 is a graph illustrating variations in voltage and
variations in voltage per unit remaining capacity or per unit time
of the secondary battery during charge at a charge rate of 0.5
(CA);
[0016] FIG. 8 is a graph illustrating variations in voltage and
variations in voltage per unit remaining capacity or per unit time
of the secondary battery during charge at a charge rate of 0.8
(CA);
[0017] FIG. 9 is a graph illustrating variations in voltage and
variations in voltage per unit remaining capacity or per unit time
of the secondary battery during charge at a charge rate of 0.9
(CA);
[0018] FIG. 10 is a graph illustrating variations in voltage and
variations in voltage per unit remaining capacity or per unit time
of the secondary battery during charge at a charge rate of 1.0
(CA);
[0019] FIG. 11 is a brief flowchart of a battery capacity
estimation sequence;
[0020] FIG. 12 is a detailed flowchart of the battery capacity
estimation sequence;
[0021] FIG. 13 is a graph illustrating variations in voltage,
variations in voltage per unit remaining capacity or per unit time,
and variations in charge current of a secondary battery during
charge at an ambient temperature of 25.degree. C. according to an
embodiment;
[0022] FIG. 14 is a table including correlation data that represent
a correlation between periods and battery capacities;
[0023] FIG. 15 is a brief flowchart of a battery capacity
estimation sequence;
[0024] FIG. 16 is a detailed flowchart of the battery capacity
estimation sequence;
[0025] FIG. 17 is a brief flowchart of a remaining capacity
estimation sequence;
[0026] FIG. 18 is a detailed flowchart of the remaining capacity
estimation sequence;
[0027] FIG. 19 a graph illustrating variations in voltage,
variations in voltage per unit remaining capacity or per unit time,
and variations in charge current of a secondary battery during
discharge at an ambient temperature of 0.degree. C. according to an
embodiment; and
[0028] FIG. 20 is a table including correlation data that represent
a correlation between periods and battery deterioration levels
(capacity retention) at different ambient temperatures according to
an embodiment.
DESCRIPTION OF EMBODIMENTS
[0029] According to a first aspect, a condition estimation device
for estimating condition of an electric storage device includes a
voltage detector and a controller. The voltage detector is
configured to detect a voltage of the electric storage device. The
controller is configured to perform a distinctive point detection
process to detect a distinctive point based on the voltage detected
by the voltage detector, and an estimation process to estimate the
condition of the electric storage device based on the distinctive
point detected in the distinctive point detection process. The
distinctive point is a point at which a variation in voltage per
unit remaining capacity or per unit time of the electric storage
device during charge or discharge is a local maximum value. The
variations in voltage per unit remaining capacity or per unit time
are variations in voltage per unit remaining capacity or per unit
time.
[0030] According to a second aspect, the controller is configured
to perform the estimation process to estimate the condition of the
electric storage device based on the voltage of the electric
storage device at which the distinctive point appears.
[0031] According to a third aspect, the controller is configured to
perform the estimation process to estimate a remaining capacity of
the electric storage device based on the distinctive point detected
in the distinctive point detection process.
[0032] According to a fourth aspect, the distinctive point includes
a plurality of distinctive points, and the controller is configured
to select one of the distinctive points in a higher voltage region
in the distinctive point detection process.
[0033] According to a fifth aspect, the controller is configured to
perform a period measurement process to measure a period from when
the distinctive point detected in the distinctive point detection
process appears until when a voltage of the electric storage device
reaches a set voltage, and perform the estimation process to
estimate the condition of the electric storage device based on the
period measured in the period measurement process.
[0034] According to a sixth aspect, the controller is configured to
detect whether the voltage of the electric storage device reaches
the set voltage based on the voltage of the electric storage device
detected by the voltage detector.
[0035] According to a seventh aspect, the set voltage is a
switching voltage at which a charge mode for charging the electric
storage device is switched.
[0036] According to an eighth aspect, the controller is configured
to perform the distinctive point detection process to determine the
distinctive point based on the variation in voltage per unit
remaining capacity or per unit time of the electric storage device
during the charge.
[0037] According to a ninth aspect, the electric storage device
includes a negative active material including graphite.
[0038] According to a tenth aspect, the controller is configured to
perform a deterioration estimating process to estimate a
deterioration level of the electric storage device.
[0039] According to an eleventh aspect, a condition estimation
method for estimating condition of an electric storage includes
detecting a distinctive point based on a voltage of the electric
storage device detected by a voltage detector, and estimating the
condition of the electric storage device based on the distinctive
point. The distinctive point is a point at which a variation in
voltage per unit remaining capacity or per unit time of the
electric storage device during charge or discharge is a local
maximum value.
[0040] The technologies described herein can be used in various
applications including a condition estimation device, a method of
estimating a condition, a computer program for executing the
function of the device or the method, or a recording medium that
stores the computer program.
[0041] According to the invention disclosed herein, the condition
of the electric storage device can be estimated without charging or
discharging the electric storage device until the electric storage
device satisfies a predetermined fully charged condition or fully
discharged condition, which was required in the known
technology.
[0042] An embodiment of the present technology will be described in
brief. In the condition estimation device, the controller is
configured to estimate the condition of the electric storage device
based on the distinctive point. The condition of the electric
storage device can be estimated when the electric storage device is
charged or discharged at least until the distinctive point appears.
The condition estimation device according to this embodiment can
estimate the condition of the electric storage device (e.g., the
battery capacity or the internal resistance) without charging or
discharging the electric storage device until the electric storage
device satisfies a predetermined fully charged condition or fully
discharged condition, which was required in the known technology.
As a result, time required for the estimation of condition of the
electric storage device can be shortened. In addition, the
controller can estimate the condition more frequently, because
requirements for the estimation of the condition are reduced.
[0043] In the condition estimation device, the controller is
configured to estimate the condition of the electric storage device
based on the voltage of the electric storage device at which the
distinctive point appears. In this configuration, after the
distinctive point appears, the electric storage device is not
required to be charged or discharged for estimating the condition.
Therefore, the time required for estimating the condition can be
shortened, and thus requirements for the estimation of the
condition can be reduced.
[0044] In the condition estimation device, the controller is
configured to estimate the condition of the electric storage device
based on a remaining capacity of the electric storage device at
which the distinctive point appears. In this configuration, the
condition of the electric storage devices that have different
battery capacities can be estimated with high accuracy, and thus
the requirements for the estimation of the condition can be
reduced.
[0045] In the condition estimation device, the distinctive point
includes a plurality of distinctive points, and the controller is
configured to select one of the distinctive points in a higher
voltage region in the distinctive point detection process. The
points at which the distinctive points appear are not much
different from one another in the high voltage region compared with
the distinctive points in the lower voltage region. Therefore, the
voltage at which the distinctive point appears and the period can
be measured with high accuracy, and thus the condition of the
electric storage device can be estimated with high accuracy.
[0046] In the condition estimation device, the condition of the
electric storage device is estimated based on the period from when
the distinctive point detected in the distinctive point detection
process appears until when the voltage of the electric storage
device reaches a set voltage. The period can be determined by
measuring the time the voltage at which the distinctive point
appears or the voltage slightly lower the voltage at which the
distinctive point appears takes to reach the set voltage.
Therefore, the controller can estimate the condition of the
electric storage device without charging or discharging the
electric storage device until the electric storage device satisfies
a predetermined fully charged condition or a fully discharged
condition, which was required in the known technology.
[0047] In the condition estimation device, the controller is
configured to determine the distinctive point based on the
variation in voltage per unit remaining capacity or per unit time
of the electric storage device during the charge. Since the charge
current is controlled by a charger, the charge current is more
stable than the discharge current supplied to the load.
Accordingly, the distinctive point can be easily detected.
[0048] In the condition estimation device, the controller is
configured to detect whether the voltage of the electric storage
device reaches the set voltage based on the voltage of the electric
storage device detected by the voltage detector. In this
configuration, the period from when the distinctive point appears
until when the voltage of the electric device reaches the set
voltage can be measured based on information including the value
detected by the voltage detector and the time. Other measurement
values are not required.
[0049] In the condition estimation device, the set voltage is a
switching voltage at which a charge mode for charging the electric
storage device is switched. The switching voltage can be detected
by the charger. If the charger is configured to transmit a
switching signal when the charge mode is switched, the condition
estimation device is not required to determine whether the electric
storage device has reached the set voltage. A processing load on
the condition estimation device can be reduced.
FIRST EMBODIMENT
[0050] A first embodiment will be described with reference to FIG.
1 to FIG. 12.
[0051] 1. Configuration of a Battery Pack
[0052] A configuration of a battery pack 60 according to this
embodiment is illustrated in FIG. 1. The battery pack 60 is
installed in an electric vehicle or a hybrid vehicle, for example,
to supply power to an electrically-powered device that operates
with electrical energy.
[0053] As illustrated in FIG. 1, the battery pack 60 includes
battery modules 10, a battery manager (hereinafter referred to as
the BM) 62, and a current sensor 64. Each battery module 10
includes an assembled battery 12 and a cell sensor (hereinafter
referred to as the CS) 20. The assembled battery 12 includes
secondary batteries (cells) 14 (see FIG. 2). The cell sensor 20 is
a board on which a sensor unit 30 and a communication circuit 28
are arranged. The BM 62 manages the battery module 10. The BM 62
and the CS 20 are an example of a condition estimation device. Each
secondary battery 14 is an example of an electric storage device. A
battery capacity X of the secondary battery 14 is an example of an
electric device condition.
[0054] The assembled batteries 12 in the battery modules 10 and the
current sensor 64 are connected in series via an electric line 68
and are connected to a charger/load 18. The charger of the
charger/load 18 is installed in an electric vehicle. The load of
the charger/load 18 is a power source, for example, and is arranged
inside the electric vehicle. The charger of the charger/load 18 is
a regular charger that can be plugged into a wall outlet. The
charger of the charger/load 18 detects a voltage of the assembled
battery 12 and charges the assembled battery 12 at a constant
current until the assembled battery 12 reaches a switching voltage.
The charger of the charger/load 18 then charges the assembled
battery 12 at a constant voltage after the assembled battery 12 has
reached the switching voltage.
[0055] The BM 62 includes a central processing unit (hereinafter
referred to as the CPU) 70 and a communication unit 74. As
illustrated in FIG. 1, the CPU 70 includes a memory 76 such as ROM
and RAM, a timer 77 configured to time, an analog-to-digital
converter (hereinafter, referred to as the ADC) 78 configured to
convert a current value I that is detected as an analog signal into
a digital value. The memory 76 stores various programs (including a
battery management program) for controlling operations of the CSs
20. The CPU 70 is configured to control components of the battery
pack 60, for example, by executing a capacity estimation sequence,
which will be described later, according to the program read out of
the memory 76. The memory 76 stores correlation data (see FIG. 4)
that represents a correlation between a voltage V at which a second
distinctive point P2 appears and a battery capacity X, which is
required for the capacity estimation sequence, for example. The CPU
70 is an example of a controller.
[0056] The communication unit 74 is connected to the CS 20, which
included in each battery module 10, via a communication line 80.
The communication unit 74 receives data such as voltages V and
temperatures D that are determined at each CS 20, which will be
described later. The CPU 70 monitors the assembled batteries 12
based on the data received by the communication unit 74 and
estimates the battery capacity X of each secondary battery 14.
[0057] The battery pack 60 also includes an operation unit (not
illustrated) for receiving inputs from a user and a liquid crystal
display (not illustrated) for displaying deterioration levels of
the assembled batteries 12 and other information.
[0058] A configuration of the battery module 10 is schematically
illustrated in FIG. 2. Each assembled battery 12 includes the
secondary batteries 14 that are rechargeable. Each CS 20 includes a
sensor unit 30 and a communication unit 28. The sensor unit 30
includes a voltage measurement circuit 24, a temperature sensor 26,
and a timer 27. The timer 27 is used for determining time to
measure the voltage V or the temperature D. The voltage measurement
circuit 24 is an example of a voltage measurement circuit.
[0059] The voltage measurement circuit 24 is connected to terminals
of each secondary battery 14 included in the assembled battery 12
and measures the voltage V (V) across the secondary battery 14
every predetermined period. The temperature sensor 26 is a
contact-type temperature sensor or a noncontact-type temperature
sensor. The temperature sensor 26 measures a temperature D
(.degree. C.) of each secondary battery 14 included in the
assembled battery 12 every predetermined period.
[0060] The communication unit 28 is connected to the BM 62 via a
communication line 80. The communication unit 28 sends information
including the voltage V and the temperature D measured by the CS 20
to the BM 62. The BM 62 stores the voltage V and the temperature D
sent by each CS 20 in the memory 76.
[0061] 2. Principle of Capacity Estimation
[0062] The battery capacity X of the secondary battery 14 decreases
as the secondary battery 14 deteriorates, and thus the battery
capacity X thereof is required to be calculated on a regular basis.
The battery capacity X corresponds to a quantity of electricity
that can be discharged from the battery during a period in which a
discharge voltage of the battery decreases from a rated voltage at
a start of discharge to a predetermined discharge cut-off voltage.
The battery capacity X is measured in ampere-hours (Ah), which is a
product of current and time.
[0063] In the secondary battery 14 such as a lithium ion secondary
battery, a distinctive point P may appear in voltages during the
charge or the discharge due to an effect of an active material in
electrodes of the battery or changes in chemical process. The
distinctive point P is a point at which a variation in voltage per
unit remaining capacity or per unit time of the secondary battery
14 during the charge or the discharge is a local maximum value.
[0064] Examples of the lithium ion secondary battery that has the
distinctive point P include a ternary lithium ion secondary battery
and an olivine iron based lithium ion secondary battery. The
ternary lithium ion secondary battery includes lithium containing
metal oxide that contains an element of Co, Mn, Ni as a positive
active material. The olivine iron based lithium ion secondary
battery includes olivine type iron phosphate as the positive active
material, i.e., lithium iron phosphate (LiFeP04). As a negative
active material, graphite or carbon may be used.
[0065] The inventors conducted experiments and studies to find out
a correlation between the battery capacity X of the secondary
battery 14 and the distinctive point P. The inventors found that
points (on a remaining capacity axis or a time axis) at which the
distinctive points P appeared were not much different from one
another when the secondary batteries 14 were charged or discharged
under the same conditions (such as at the same charging rate)
although the secondary batteries 14 had different capacities. A
graph in FIG. 3 has a horizontal axis representing a remaining
capacity (a remaining capacity axis) and a vertical axis
representing a voltage. In FIG. 3, a variation in voltage V and a
variation in voltage per unit remaining capacity .DELTA.V during
charge of a lithium ion secondary battery that has an initial
capacity of 50 Ah from the SOC of 0 (%) at the rate of 0.2 (CA)
under an ambient temperature of 25.degree. C. are represented. The
lithium ion battery is, specifically, a ternary lithium ion
secondary battery that includes the lithium containing metal oxide
that contains an element of Co, Mn, Ni as a positive active
material and the graphite as the negative positive material.
[0066] In an example illustrated in FIG. 3, a first distinctive
point P1 appears in a low voltage region of about 3.6 (V) to 3.8
(V) and a second distinctive point P2 appears in a high voltage
region of about 3.95 (V) to 4.06 (V). Voltages at the positive
electrode and voltages at the negative electrode of the lithium ion
secondary battery 14 were separately measured and the variations
.DELTA.V were determined. Distinctive points in the cases of the
positive electrode and the negative electrode are referred to as
distinctive points P in the following description. In the case of
the positive electrode, the distinctive point P appeared about the
first distinctive point P1 (about the remaining capacity of about
10000 (mAh) in the example in FIG. 3). In the case of the negative
electrode, the distinctive point P appeared about the second
distinctive point P2 (about the remaining capacity of about 31000
(mAh) in the example in FIG. 3). Accordingly, it is assumed that
the first distinctive point P1 appears due to the influence of the
positive active material and the distinctive and the second
distinctive point P2 appears due to the influence of the negative
active material.
[0067] In the high voltage region, the points (on the remaining
capacity axis or the time axis) at which the second distinctive
points P2 appear are not much different from one another although
batteries have different battery capacities X. In the cases of
three lithium ion secondary batteries 14A to 14C that have
different battery capacities X, the second distinctive points P2
appear about the remaining capacity of 31000 (mAH). Specifically,
the second distinctive point P2 appears at the remaining capacity
of 30750 (mAH) in the case of the lithium ion secondary battery
14A, the second distinctive point P2 appears at the remaining
capacity of 31000 (mAH) in the case of the lithium ion secondary
battery 14B, and the second distinctive point P2 appears at the
remaining capacity of 31410 (mAH) in the case of the lithium ion
secondary battery 14C.
[0068] The lithium ion secondary battery 14A is a deteriorated
battery that has the battery capacity X of 39.9 (Ah) and a capacity
retention rate of 79.8 (%). The lithium ion secondary battery 14B
is a deteriorated battery that has the battery capacity X of 44.55
(Ah) and a capacity retention rate of 89.1 (%). The lithium ion
secondary battery 14C is a new battery that has the battery
capacity X of 50 (Ah) and a capacity retention rate of 100 (%).
[0069] When the battery capacity X becomes smaller, the voltage of
the secondary battery 14 increases more rapidly during the charge.
If the lithium ion secondary batteries 14 that have different
battery capacities X are charged at the same charging rate, the
second distinctive points P2 appear at different voltages.
[0070] More specifically described, as illustrated in FIG. 3, the
second distinctive point P2 appears at the voltage of 3.9804 (V) in
the case of the secondary battery 14C, and the second distinctive
point P2 appears at the voltage of 4.0119 (V) in the case of the
secondary battery 14B. Further, the second distinctive point P2
appears at the voltage of 4.0577 (V) in the case of the secondary
battery 14A. The smaller the battery capacity X of the secondary
battery 14, the higher the voltage at which the second distinctive
point P2 appears. The charging rate is a rate calculated based on
an amount of charging current relative to an initial capacity of a
battery.
[0071] By measuring the voltage V at which the second distinctive
point P2 appears, the battery capacity X of the secondary battery
14 can be estimated. For example, experiments may be conducted for
measuring voltages of the secondary batteries 14 having different
battery capacities X at which the second distinctive points P2
appear during charge of the secondary batteries 14 from 0% SOC.
Then, correlation data that contains the voltages V at which the
second distinctive points P2 appear in association with the battery
capacities X of the secondary batteries 14 (see FIG. 4) may be
created. A battery capacity X of a secondary battery 14 can be
estimated based on the correlation data.
[0072] A graph in FIG. 5 has a remaining capacity axis as a
horizontal axis and a voltage axis as a vertical axis. In FIG. 5, a
variation in voltage V and a variation in voltage per unit
remaining capacity .DELTA.V during discharge of a lithium ion
secondary battery that has an initial capacity of 50 Ah from the
SOC of 100 (%) at the rate of 0.2 (CA) under an ambient temperature
of 25.degree. C. are represented. Similar to the example in FIG. 3,
the lithium ion secondary battery 14A is a deteriorated battery
that has the battery capacity X of 39.9 (Ah) and a capacity
retention rate of 79.8 (%). The lithium ion secondary battery 14B
is a deteriorated battery that has the battery capacity X of 44.55
(Ah) and a capacity retention rate of 89.1 (%). The lithium ion
secondary battery 14C is a new battery that has the battery
capacity X of 50 (Ah) and a capacity retention rate of 100 (%).
[0073] As illustrated in FIG. 5, during discharge of the secondary
battery 14, the smaller the battery capacity X of the secondary
battery 14, the higher the voltage at which the second distinctive
point P2 appears, which is the same tendency exhibited during
charge of the secondary battery 14. However, during discharge, the
voltage at which the distinctive point appears is 3.9375 (V) in the
case of the secondary battery 14C, 3.9628 (V) in the case of the
secondary battery 14B, and 3.9920 (V) in the case of the secondary
battery 14A, that is, the voltage tends to be lower than the
voltage at which the second distinctive point P2 appears during
charge. Therefore, different pieces of the correlation data as in
FIG. 4 may be prepared for the case of charging and that of
discharging.
[0074] As illustrated in FIG. 5, the remaining capacity at which
the second distinctive point P2 appears during discharge tends to
be larger than the remaining capacity at which the second
distinctive point P2 appears during charge. Specifically, the
second distinctive point P2 appears at the remaining capacity of
33000 (mAH) in the case of the lithium ion secondary battery 14A,
the second distinctive point P2 appears at the remaining capacity
of 33250 (mAH) in the case of the lithium ion secondary battery
14B, and the second distinctive point P2 appears at the remaining
capacity of 33830 (mAH) in the case of the lithium ion secondary
battery 14C.
[0075] A correlation between the charging rate and the second
distinctive point P2 were examined based on voltages of the lithium
ion secondary battery 14 having a capacity of 50 Ah (more
specifically, the ternary lithium ion secondary battery) measured
while the secondary battery 14 was charged at different charging
rates under the ambient temperature of 25.degree. C. As illustrated
in FIGS. 6 to 10, the second distinctive points P2 clearly appeared
when the secondary battery 14 was charged at the charging rate in a
rage from 0.2 (CA) to 0.9 (CA) while a noticeable second
distinctive point P2 did not appear when the secondary battery 14
was charged at the charging rate of 1 (CA). Namely, a lower
charging rate is preferable and a charging rate of 0.9 (CA) or
lower is preferable.
[0076] 3. Determination of Distinctive Point
[0077] As illustrated in FIG. 3 or FIG. 5, there are multiple
distinctive points, the first distinctive point P1 and the second
distinctive point P2. If a distinctive point P is detected based on
the variation .DELTA.V, it is required to determine whether the
distinctive point P is the second distinctive point P2.
[0078] Whether the distinctive point P is the second distinctive
point P2 can be determined based on a startup voltage V.sub.O that
is a voltage at a start of charge. Specifically, if the startup
voltage V.sub.O is lower than a voltage V1 at which the first
distinctive point P1 appears, the first distinctive point P1
appears after the charge is started and then the second distinctive
point P2 appears. Therefore, the distinctive point P that appears
second is determined as the second distinctive point P2. If the
startup voltage V.sub.O is between the voltage V1 at which the
first distinctive point P1 appears and a voltage V2 at which the
second distinctive point P2 appears, the first distinctive point P1
does not appear after the charge is started and only the second
distinctive point P2 appears. Therefore, the distinctive point P
that appears first is determined as the second distinctive point
P2. Whether the distinctive point P is the second distinctive point
P2 can be determined based on another parameter having a
correlation with a voltage other than the startup voltage V.sub.O,
such as an SOC or a remaining capacity at a start of charge.
[0079] 4. Capacity Estimation Sequence
[0080] Next, a capacity estimation sequence for estimating the
battery capacity X of the secondary battery 14 will be described
with reference to FIGS. 11 and 12. The capacity estimation sequence
is executed by the CPU 70 in the BM 62 during the charge of the
secondary battery 14.
[0081] The CPU 70 determines whether the charge of the secondary
battery 14 by the charger of the charger/load 18 is started (S100).
If the charge is not started (NO in step S100), the CPU 70 waits
until the charge is started. If the charge is started (YES in step
S100), the CPU 70 controls the CS 20 to start measurement of a
voltage V and measurement of a temperature D (S10, S110) of the
secondary battery 14. The measurement of the voltage V and that of
the temperature D are repeatedly performed in a predetermined
cycle. The CPU 70 controls the CS 20 to transmit information
including the measured voltage V and the measured temperature D
together with information including time at which the measurement
is performed to the BM 62 via the communication line 80. The CPU 70
converts the information including the voltage V (e.g., V3) and the
temperature D transmitted to the BM 62 to digital data in the ADC
78, and stores the digital data with the information including the
time (e.g., t3) in the memory 76 (S110). Steps S100 and S110 in
FIG. 12 correspond to the step for starting the voltage measurement
(S10) in FIG. 11.
[0082] When the CPU 70 receives the information including the
voltage V and the temperature D of the secondary battery 14 from
the CS 20, the CPU 70 starts detection of the distinctive point P
(S20). Specifically, the CPU 70 determines whether time (reference
time) to control the CS 20 for the next measurement of the voltage
V and that of the temperature D of the secondary battery 14 has
passed after the CPU 70 has received the information including the
voltage V and the temperature D of the secondary battery 14 from
the CS 20 (S120). If the time has not passed (NO in step S120), the
CPU 70 waits until the time passes. If the time has passed (YES in
step S120), the CPU 70 controls the CS 20 to perform the
measurement of the voltage V and that of the temperature D (S130).
The CPU 70 converts the information including the voltage V (e.g.,
V4) and the temperature D transmitted to the BM 62 to digital data
in the ADC 78, and stores the digital data with the information
including the time (e.g., t4) in the memory 76 (S130).
[0083] The CPU 70 reads the data on the voltages of the secondary
battery 14 (e.g., V3 and V4) and data on the measurement time t at
which the measurement is performed (e.g., t3 and t4) out of the
memory 76. The CPU 70 calculates the variation .DELTA.V at each
time t (see Equation 1 below) (S140). Then, the CPU 70 compares the
variations .DELTA.V for the times t to determine if each variation
.DELTA.V is a local maximum value (S150). If the variation .DELTA.V
is not the local maximum value (NO in step S150), the process
returns to the step S110. If the variation .DELTA.V is the local
maximum value (YES in step S150), the CPU 70 detects the second
distinctive point P2 that is the local maximum value in the high
voltage region according to the above-described method
(determination based on the startup voltage Vo) and detects the
voltage at which the second distinctive point P2 appears (S160).
Steps S20 corresponds to a distinctive point detection process and
a step for detecting a distinctive point. Steps 120 to 150 in FIG.
12 correspond to the step for detecting the distinctive point (S20)
in FIG. 11.
.DELTA.V=(V4-V3)/(t4-t3) (1)
[0084] In the above, the CPU 70 detects the distinctive point P
based on calculation of the local maximum value of the variation
.DELTA.V per unit time, but may detect the distinctive point P
based on calculation of the local maximum value of the variation
.DELTA.V per unit remaining capacity.
[0085] After the CPU 70 detects the second distinctive point P2 and
the voltage at which the second distinctive point P2 appears, the
CPU 70 reads the correlation data out of the memory 76 (S170), and
then estimates the battery capacity X of the secondary battery 14
(S40, S180). Specifically, the CPU 70 refers to the correlation
data for the voltage, which is detected in step S20, at which the
second distinctive point P2 appears and estimates that the battery
capacity X that is in association with the voltage V as the battery
capacity X of the secondary battery 14. For example, if the voltage
V at which the second distinctive point P2 appears is Va in FIG. 4,
the CPU 70 estimates the battery capacity X of the secondary
battery 14 as Xa. Then, when the secondary battery 14 is fully
charged, the CPU 70 ends the capacity estimation sequence. Step 40
corresponds to the estimation process and the estimation step.
Steps 160 to 180 in FIG. 12 correspond to the battery capacity
estimation (S40) in FIG. 11.
[0086] 5. Effects of the Embodiment
[0087] In the BM 62 according to this embodiment, the CPU 70
estimates the battery capacity X of the secondary battery 14 based
on the voltage of the secondary voltage 14 at which the distinctive
point P appears. Thus, when the charge is started from the startup
voltage Vo, the CPU 70 is required to charge the secondary battery
14 at least until the second distinctive point P2 appears. However,
after the second distinctive point P2 appears, the charge of the
secondary battery 14 is not required. The CPU 70 can estimate the
battery capacity X of the secondary battery 14 without charging or
discharging the secondary battery 14 until the secondary battery 14
satisfies a predetermined fully charged condition or a fully
discharged condition, which was required in the known technology.
As a result, time required for the estimation of the battery
capacity X can be shortened. In addition, the CPU 70 can estimate
the battery capacity more frequently, because requirements for the
estimation of the battery capacity X are reduced.
[0088] In the BM 62 according to this embodiment, the CPU 70
selects the second distinctive point P2 in the high voltage region
and estimates the battery capacity X if the distinctive point P
includes the distinctive points P1, P2. The CPU 70 can correctly
determine the voltage V at which the distinctive point appears,
because the second distinctive points P2 in the high voltage region
appear at points that are not much different from one another
compared with the first distinctive points P1 in the low voltage
region. Therefore, the CPU 70 can correctly estimate the battery
capacity X of the secondary battery 14.
[0089] In the BM 62 according to this embodiment, the CPU 70
determines the distinctive point P based on the variation in
voltage during the charge. Since the charge current is controlled
by the charger 18, the charge current is more stable than the
discharge current supplied to the load. Therefore, the CPU 70 can
easily detect the distinctive point P.
SECOND EMBODIMENT
[0090] According to the first embodiment, the CPU 70 estimates the
battery capacity X of the secondary battery 14 based on the voltage
of the secondary battery 14 at which the distinctive point P
appears. According to the second embodiment, the CPU 70 estimates
the battery capacity X of the secondary battery 14 based on a
period T from when the distinctive point P appears until when the
secondary battery 14 reaches a set voltage.
[0091] More specifically described, as described in the first
embodiment, the points at which the distinctive points P appear (on
the remaining capacity axis or the time axis) are not much
different from one another when the secondary batteries 14 are
charged or discharged under the same condition (such as at the same
charging rate) although the secondary batteries 14 have different
capacities X. A graph in FIG. 13 has a horizontal axis representing
a time and a vertical axis representing a voltage and a current. In
FIG. 13, a variation in voltage V and a variation in voltage per
unit time .DELTA.V during charge of a lithium ion secondary battery
that has an initial capacity of 50 Ah from the SOC of 0 (%) at the
rate of 0.2 (CA) are represented.
[0092] When the battery capacity X becomes smaller, the voltage of
the secondary battery 14 increases more rapidly during the charge.
If the lithium ion secondary batteries 14 that have different
battery capacities X are charged at the same charging rate, as
illustrated in FIG. 13, the secondary batteries 14 reach the
predetermined set voltage at different times. In examples in FIG.
13, the secondary battery 14C reaches the set voltage of 4.1 (V) at
a time tc. The secondary battery 14B reaches the set voltage of 4.1
(V) at a time tb and the secondary battery 14A reaches the set
voltage of 4.1 (V) at a time ta. The smaller the battery capacity
X, the sooner the secondary battery 14 reaches the set voltage.
Periods from the time t2 at which the second distinctive point P2
appears until when the secondary batteries 14A to 14C reach the set
voltage are referred to as periods TA to TC, respectively. The
periods TA to TC may be correctively referred to as the period
T.
[0093] As can be seen from the above, the smaller the battery
capacity X of each secondary battery 14A to 14C, the shorter the
periods TA to TC from the time t2 at which the second distinctive
point P2 appears until when the secondary battery 14 reaches the
set voltage. By measuring the period T, the battery capacity X of
the secondary battery 14 can be estimated. For example, experiments
may be conducted for measuring the periods T using the secondary
batteries 14 having different battery capacities X. Then,
correlation data that contains the periods T in association with
the battery capacities X of the secondary batteries 14 (see FIG.
14) may be created. A battery capacity X of a secondary battery 14
can be estimated based on the correlation data.
[0094] In the above embodiment, the set voltage was 4.1 (V).
However, the set voltage is not limited to 4.1 (V) and may be other
values. Specifically, if the period T is measured based on the
variations in voltage during the charge, the set voltage may be any
voltage that is higher than the voltage at which the distinctive
point P appears. In this embodiment, the second distinctive point
P2 appears in a region of 3.95 (V) to 4.05 (V), and thus any
voltage higher than 4.05 (V) may be used as the set voltage.
[0095] If the period T is measured based on the variations in
voltage during the discharge, the set voltage may be any voltage
that is lower than the voltage at which the distinctive point P
appears. In this embodiment, the second distinctive point P2
appears in a region of 3.95 (V) to 4.05 (V), and thus any voltage
lower than 3.95 (V) may be used as the set voltage.
[0096] Next, a capacity estimation sequence for estimating the
battery capacity X of the secondary battery 14 will be described
with reference to FIGS. 15 and 16. The capacity estimation sequence
is executed by the CPU 70 in the BM 62 during the charge of the
secondary battery 14.
[0097] The CPU 70 determines whether the charge of the secondary
battery 14 by the charger of the charger/load 18 is started (S100).
If the charge is not started (NO in step S100), the CPU 70 waits
until the charge is started. If the charge is started (YES in step
S100), the CPU 70 controls the CS 20 to start measurement of a
voltage V and measurement of a temperature D (S10, S110) of the
secondary battery 14. The measurement of the voltage V and that of
the temperature D are repeatedly performed in a predetermined
cycle. The CPU 70 controls the CS 20 to transmit information
including the measured voltage V and the measured temperature D
together with information including time at which the measurement
is performed to the BM 62 via the communication line 80. The CPU 70
converts the information including the voltage V (e.g., V3) and the
temperature D transmitted to the BM 62 to digital data in the ADC
78, and stores the digital data with the information including the
time (e.g., t3) in the memory 76 (S110). Steps S100 and S110 in
FIG. 16 correspond to the step for starting the voltage measurement
(S10) in FIG. 15.
[0098] When the CPU 70 receives the information including the
voltage V and the temperature D of the secondary battery 14 from
the CS 20, the CPU 70 starts detection of the distinctive point P
(S20). Specifically, the CPU 70 determines whether time (reference
time) to control the CS 20 for the next measurement of the voltage
V and that of the temperature D of the secondary battery 14 has
passed after the CPU 70 has received the information including the
voltage V and the temperature D of the secondary battery 14 from
the CS 20 (S120). If the time has not passed (NO in step S120), the
CPU 70 waits until the time passes. If the time has passed (YES in
step S120), the CPU 70 controls the CS 20 to perform the
measurement of the voltage V and that of the temperature D (S130).
The CPU 70 converts the information including the voltage V (e.g.,
V4) and the temperature D transmitted to the BM 62 to digital data
in the ADC 78, and stores the digital data with the information
including the time (e.g., t4) in the memory 76 (S130).
[0099] The CPU 70 reads the data on the voltages V of the secondary
battery 14 (e.g., V3 and V4) and data on the time t at which the
measurement is performed (e.g., t3 and t4) out of the memory 76.
The CPU 70 calculates the variation .DELTA.V at each time t (see
Equation 1 of the first embodiment) (S140). Then, the CPU 70
compares the variations .DELTA.V at each measurement time t to
determine if each variation .DELTA.V is a local maximum value
(S150). If the variation .DELTA.V is not the local maximum value
(NO in step S150), the process returns to the step S110. If the
variation .DELTA.V is the local maximum value (YES in step S150),
the CPU 70 detects the second distinctive point P2 that is the
local maximum value in the high voltage region and the voltage at
which the second distinctive point P2 appears according to the
above-described method (determination based on the startup voltage
Vo) (S160). Step S20 corresponds to a distinctive point detection
process, a step for detecting a distinctive point. Steps 120 to 150
in FIG. 16 correspond to a step for detecting a distinctive point
(S20) in FIG. 15.
[0100] Then, the CPU 70 compares the voltage V of the secondary
battery 14 measured by the CS 20 with the set voltage (e.g., 4.1
(V)) (S210), and measures the period T from the time t2 when the
second distinctive point P2 appears until when the secondary
battery 14 reaches the set voltage. Specifically, the CPU 70
obtains the time when the secondary battery 14 reaches the set
voltage based on the result of the comparison and the period
measured by the timer 27 to measure the period T from the time t2
when the second distinctive point P2 appears until when the
secondary battery 14 reaches the set voltage. S30 corresponds to a
period determination process.
[0101] More specifically described, the CPU 70 starts the
measurement of the period T (S200) and determines whether the
voltage V of the secondary battery 14 has reached the set voltage
(S210). If the voltage V of the secondary battery 14 has not
reached the set voltage (NO in step S210), the process returns to
the step 5200. If the voltage V of the secondary battery has
reached the set voltage (YES in step S210), the CPU 70 ends the
measurement of the period T (S220). Steps 160 to 220 in FIG. 16
correspond to the period measurement (S30) in FIG. 15.
[0102] After the measurement of the period T, the CPU 70 reads the
correlation data out of the memory 76 (S170), and estimates the
battery capacity X of the secondary battery 14 (S40, S180).
Specifically, the CPU 70 refers to the correlation data for the
periods T and estimates the battery capacity X that is in
association with each period T as the battery capacity X of the
secondary battery 14. For example, if the period T is T1 in FIG.
14, the CPU 70 estimates the battery capacity X of the secondary
battery 14 as X1. Then, when the secondary battery 14 is fully
charged, the CPU 70 ends the capacity estimation sequence. Step 40
corresponds to the estimation process and the estimation step.
Steps 170 to 180 in FIG. 16 correspond to the battery capacity
estimation (S40) in FIG. 15.
[0103] In the BM 62 according to this embodiment, the CPU 70
estimates the battery capacity X of the secondary battery 14 based
on the period T from when the distinctive point P appears until
when the secondary battery 14 reaches the set voltage. The CPU 70
can determine the period T by measuring a period from when the
secondary battery 14 is at a voltage slightly lower than the
distinctive point P and when the secondary battery reaches the set
voltage. The CPU 70 can estimate the battery capacity X of the
secondary battery 14 without charging or discharging the secondary
battery 14 until the secondary battery 14 satisfies the fully
discharged condition or the fully charged condition, which was
required in the known technology. As a result, the time required
for the estimation of the battery capacity X can be shortened. In
addition, the CPU 70 can estimate the battery capacity more
frequently, because requirements for the estimation of the battery
capacity X are reduced.
[0104] In the BM 62 according to this embodiment, the CPU 70
determines the second distinctive point P2 in the high voltage
region as a reference distinctive point. The period is measured
based on the reference distinctive point. The second distinctive
point P2 in the high voltage region is proper as the reference for
measuring the period, because the second distinctive points P2 in
the high voltage region appear at points that are not much
different from one another compared with the first distinctive
points P1 in the low voltage region. A difference in the period T
depending on the capacity is clearer when the period T is measured
based on the second distinctive points P2 that appears at points
that are not much different from one another. With this
configuration, the CPU 70 can correctly estimate the battery
capacity X of the secondary battery 14.
[0105] The CS 20 measures the voltage of the secondary battery 14
every predetermined period. The BM 62 monitors the condition of the
secondary battery 14 based on the value measured by the CS 20. In
the BM 62 according to this embodiment, the CPU 70 determines
whether the voltage V of the secondary battery 14 has reached the
set voltage based on the value (the voltage of the secondary
battery 14) measured by the CS 20. In this configuration, the
period T from the time t2 when the second distinctive point P2
appears and until when the voltage V of the secondary battery 14
reaches the set voltage can be calculated based on the data that
has been measured by the CS 20 and the BM 62 (information including
the voltage V of the secondary battery 14 and the time at which the
measurement is performed). The MB 62 is not required to measure
other values.
THIRD EMBODIMENT
[0106] In the second embodiment, the CPU 70 compares the voltage V
of the secondary battery 14 measured by the CS 20 to the set
voltage (e.g., 4.1 (V)) to measure the period T from the time t2
when the second distinctive point P2 appears until when the
secondary battery 14 reaches the set voltage. In the third
embodiment, the period T is measured by using a switching signal Sr
that informs the switch of the charge mode.
[0107] Specifically, the charge mode of the charger of the
charge/load 18 is CC/CV (constant current/constant voltage)
charging mode. The CPU 70 switches the charge mode from the
constant current charging mode to the constant voltage charging
mode when the secondary battery 14 reaches the switching voltage
(e.g., 4.1 (V)).
[0108] In the third embodiment, the CPU 70 sets the set voltage at
the same voltage as the switching voltage and controls the charger
of the charger/load 18 to transmit the switching signal Sr for
informing the BM 62 that the charge mode is switched, i.e., the
secondary battery 14 has reached the voltage of 4.1 (V).
[0109] In this configuration, like the second embodiment, after the
CPU 70 detects the time t2 when the second distinctive point P2
appears based on the voltage V of the secondary battery 14 measured
by the CS 20, the CPU 70 can measure the period T only by
controlling the timer 77 to measure the period from a time t2 when
the second distinctive point P2 appears until when the switching
signal Sr is received.
[0110] In the third embodiment, the BM 62 is not required to
determine whether the secondary battery 14 has reached the set
voltage, because the CPU 70 measures the period T by using the
switching signal Sr. A processing load on the BM 62 can be
reduced.
FOURTH EMBODIMENT
[0111] In the first embodiment, the CPU 70 estimates the battery
capacity X of the secondary battery 14 based on the voltage of the
secondary battery 14 at which the distinctive point P appears. In
the fourth embodiment, the CPU 70 estimates a remaining capacity at
which the second distinctive point P2 appears and determines the
remaining capacity as a remaining capacity of the secondary battery
14.
[0112] Specifically, as described in the first embodiment with
reference to FIGS. 3 and 5, the points (on the remaining capacity
axis or the time axis) at which the second distinctive points P2
appear are not much different from one another when the secondary
batteries 14 are charged or discharged under the same conditions
(such as the same charging rate) although the secondary batteries
14 have different capacities X. Specifically, in the case of
charge, a difference between the remaining capacity of the
secondary battery 14A, which has the smallest remaining capacity,
and the remaining capacity of the secondary battery 14C, which has
the largest remaining capacity, is 660 (mAh). In the case of
discharge, the a difference between the remaining capacity of the
secondary battery 14A, which has the smallest remaining capacity,
and the remaining capacity of the secondary battery 14C, which has
the largest remaining capacity, is 850 (mAh). If a reference
capacity (battery capacity) is 50000 (mAh), the CPU 70 can estimate
the remaining capacity within a small tolerance of about 2%.
[0113] In this configuration, the CPU 70 can estimate the remaining
capacity of the secondary battery 14 with high accuracy by
estimating the remaining capacity at which the second distinctive
point P2 appears as the remaining capacity of the secondary battery
14. For example, experiments are performed for the secondary
batteries 14 having different battery capacities X. Specifically,
the secondary batteries 14 are each charged from a SOC of 0 (%) to
determine the point at which the second distinctive point P2
appears, and then the remaining capacity at which the second
distinctive point P2 appears is set as a fixed value Z. The fixed
value Z can be determined as the remaining capacity of the
secondary battery 14. It is preferable that the fixed value Z is
the smallest one of the remaining capacities obtained in the
experiments to have less risk of overestimating the remaining
capacity, which may result in a sudden stop of the load driven by
the secondary battery 14 (hereinafter, referred to as a lack of
electricity).
[0114] The remaining capacities of the secondary batteries 14 at
which the second distinctive points P2 appear are smaller in FIG. 3
than in FIG. 5 by 2000 (mAh) when the secondary batteries 14 having
the same battery capacities X are compared. In view of this, two
experiments are performed by using the secondary batteries 14 that
have different battery capacities X. In one of the experiments, the
secondary battery 14 is charged from a SOC of 0 (%) to measure the
remaining capacity of the secondary battery 14 at which the second
distinctive point P2 appears. In the other one of the experiments,
the secondary battery 14 is discharged from a SOC of 100 (%) to
measure the remaining capacity of the secondary battery 14 at which
the second distinctive point P2 appears. It is preferable that a
ratio W of the remaining capacities at which the second distinctive
points P2 appear during the charge to during the discharge is
calculated for the secondary batteries 14 having the same battery
capacity X. The remaining capacity of the secondary battery 14
during the charge and the discharge can be estimated by calculating
a product of the fixed value Z and the ratio W. It is preferable
that the ratio W is the smallest one of the ratios obtained in the
experiments to have less risk of the lack of electricity.
[0115] Next, a capacity estimation sequence for estimating the
battery capacity X of the secondary battery 14 will be described
with reference to FIG. 17 and FIG. 18. The capacity estimation
sequence is executed by the CPU 70 in the BM 62 during the charge
of the secondary battery 14.
[0116] Specifically, the CPU 70 determines whether the charge of
the secondary battery 14 by the charger of the charger/load 18 is
started (S100). If the charge by the charger 18 is not started (NO
in step S100), the CPU 70 waits until the charge is started. If the
charge by the charger 18 is started (YES in step S100), the CPU 70
controls the CS 20 to start measurement of a voltage V and
measurement of a temperature D (S10, S110) of the secondary battery
14. The measurement of the voltage V and that of the temperature D
of the secondary battery 14 are repeatedly performed in a
predetermined cycle by the CS 20. The CPU 70 controls the CS 20 to
transmit information including the measured voltage V and the
measured temperature D together with information including the
remaining capacity to the BM 62 via the communication line 80. The
CPU 70 converts the information including the voltage V (e.g., V3)
and the temperature D transmitted to the BM 62 to digital data in
the ADC 78, and stores the digital data with the information
including the remaining capacity (e.g., z4) in the memory 76
(S110). Steps S100 and S110 in FIG. 18 correspond to the step for
starting the voltage measurement (S10) in FIG. 17.
[0117] When the CPU 70 receives the information including the
voltage V and the temperature D of the secondary battery 14 from
the CS 20, the CPU 70 starts detection of the distinctive point P
(S20). Specifically, the CPU 70 determines whether the remaining
capacity (reference remaining capacity) to control the CS 20 for
the next measurement of the voltage V and that of the temperature D
of the secondary battery 14 has been exceeded after the CPU 70 has
received the information including the voltage V and the
temperature D of the secondary battery 14 from the CS 20 (S300). If
the reference remaining capacity has not been exceeded (NO in step
S300), the CPU 70 waits until the reference remaining capacity is
exceeded. If the reference remaining capacity has been exceeded
(YES in step S300), the CPU 70 controls the CS 20 to perform the
measurement of the voltage V and that of the temperature D (S130).
The CPU 70 converts the information including the voltage V (e.g.,
V4) and the temperature D transmitted to the BM 62 to digital data
in the ADC 78, and stores the digital data with the information
including the remaining capacity (e.g., z4) in the memory 76
(S130).
[0118] The CPU 70 reads the data on the voltages V of the secondary
battery 14 and data on a measurement data on the remaining capacity
z at the voltage V (e.g., z3 and z4) out of the memory 76 to
calculate the variation .DELTA.V at each remaining capacity z (see
Equation 2 below) (S140). Then, the CPU 70 compares the variations
.DELTA.V at the remaining capacities z to determine if each
variation .DELTA.V is a local maximum value (S150). If the
variation .DELTA.V is not the local maximum value (NO in step
S150), the process returns to the step S110. If the variation
.DELTA.V is the local maximum value (YES in step S150), the CPU 70
detects the second distinctive point P2 that is the local maximum
value in the high voltage region and the remaining capacity at
which the second distinctive point P2 appears according to the
above-described method (determination based on the startup voltage
Vo) (S160). Step S20 corresponds to a distinctive point detection
process and a step for detecting a distinctive point. Steps 120 to
150 in FIG. 18 correspond to the step for detecting the distinctive
point (S20) in FIG. 17.
.DELTA.V=(V4-V3)/(z4-z3) (2)
[0119] Then, the CPU 70 reads the fixed value Z out of the memory
76 (S360) and estimates the remaining capacity of the secondary
battery 14 (S370). Steps 360 to 370 in FIG. 18 correspond to the
step for estimating the remaining capacity (S50) in FIG. 17.
[0120] In the BM 62 according to this embodiment, the CPU 70
estimates the remaining capacity at which the second distinctive
point P2 appears as the remaining capacity of the secondary battery
14. In this configuration, the CPU 70 can estimate the remaining
capacity of the secondary battery 14 having the battery capacity X
that is unknown. As a result, the CPU 70 can estimate the battery
capacity more frequently, because requirements for the estimation
of the remaining capacity are reduced.
OTHER EMBODIMENTS
[0121] The present invention is not limited to the embodiment
described above and illustrated in the drawings. The following
various embodiments are also included in the technical scope of the
present invention.
[0122] (1) The lithium-ion secondary battery is used as an example
of an electric storage device in the above first to fourth
embodiments. However, the electric storage device is not limited to
the lithium-ion secondary battery. The electric storage device may
be secondary batteries other than the lithium-ion battery, or
capacitors that exhibit electrochemical phenomenon.
[0123] (2) In the above second embodiment, the battery capacity X
of the secondary battery 14 is estimated based on the measurement
of the voltage during the charge of the secondary battery 14.
However, the battery capacity X of the secondary battery 14 may be
estimated based on the measurement of the voltage during the
discharge of the secondary battery 14. Specifically, the
distinctive point P or the period T may be detected based on the
variations .DELTA.V during the discharge or based on the voltage V
during the discharge. Information regarding time such as a
measurement time, which is used for the measurement of the period
T, may be provided by an external device. The variation .DELTA.V
may be a variation in voltage per unit remaining capacity.
[0124] (3) In the above first to fourth embodiments, the charger of
the charger/load 18 is a constant current/constant voltage charger.
However, the charger 18 may be a constant power/constant voltage
charger.
[0125] (4) In the above first to fourth embodiments, the CPU 70 is
used as an example of a controller. The controller may include a
plurality of CPUs, a hardware circuit such as an application
specific integrated circuit (ASIC), or both of the hardware circuit
and the CPU. Namely, the controller can have any configuration as
long as the capacity estimation sequence is executed through
software processing or using a hardware circuit.
[0126] (5) In the first embodiment, the battery capacity X of the
secondary battery 14 is estimated based on the correlation data
(FIG. 4) that contains the voltages V at which the second
distinctive points P2 appear in association with the battery
capacities X of the secondary batteries 14.
[0127] As will be described later, the voltage V at which the
second distinctive point P2 appears differs depending on the
ambient temperature although the secondary batteries 14 have the
same capacity X. The voltage V tends to be smaller as the ambient
temperature decreases. Therefore, it is preferable that the
correlation data that contains the voltages V at which the second
distinctive points P2 appear in association with the battery
capacities X of the secondary batteries 14 (the correlation data in
FIG. 14) is prepared for different ambient temperatures.
[0128] In FIG. 19, variations in voltage V and variations in
voltage per unit remaining capacity .DELTA.V during discharge of
the secondary batteries, which is the same secondary batteries as
the secondary batteries 14A, 14B in FIG. 3, from the SOC of 100 (%)
at the rate of 0.2 (CA) under an ambient temperature of 0.degree.
C. are represented. As illustrated in FIG. 3, under the ambient
temperature of 25.degree. C., the second distinctive point P2
appears at the voltage V of 4.0577 (V) in the secondary battery 14A
and at the voltage V of 4.0119 (V) in the secondary battery 14B. As
illustrated in FIG. 19, under the ambient temperature of 0.degree.
C., the second distinctive point P2 appears at the voltage V of
4.0524 (V) in the secondary battery 14A and at the voltage V of
4.0078 (V) in the secondary battery 14B. As can be seen from this,
the voltages V at which the second distinctive points P2 appear in
the batteries differ from one another depending on the ambient
temperature although the secondary batteries have the same battery
capacity X. The voltage V tends to be smaller as the ambient
temperature decreases. The same tendency is exhibited during the
discharge and the charge. Therefore, it is preferable that the
correlation data that contains the voltages V at which the second
distinctive points P2 appear in association with the battery
capacities X of the secondary batteries 14 (the correlation data in
FIG. 14) is prepared for different ambient temperatures.
[0129] (6) In the second embodiment, the battery capacity X of the
secondary battery 14 is estimated based on the correlation data
(FIG. 14) that contains the periods T in association with the
battery capacities X of the secondary batteries 14. As illustrated
in FIG. 20, the correlation data is prepared for different ambient
temperatures. The period T from when the distinctive point P
appears until when the voltage of the secondary battery 14 reaches
the set voltage is affected by internal resistance r of the
secondary battery 14. A value of the internal resistance r changes
depending on the ambient temperature. If the correlation data is
prepared for different ambient temperatures as described above, the
battery deterioration level (capacity retention rate) can be
correctly estimated. In the secondary batteries 14 that have the
same capacity retention rate, the period T becomes shorter as the
ambient temperature decreases. This is based on the following.
V=E+r.times.I (3)
where V is a terminal voltage of the secondary battery 14, E is an
open voltage of the secondary battery 14, r is an internal
resistance of the secondary battery, and I is a charge current of
the secondary battery 14.
[0130] The internal resistance r of the secondary battery 14
differs depending on the ambient temperature. The internal
resistance r of the secondary battery 14 becomes larger as the
ambient temperature decreases. In the secondary batteries 14 that
have the same capacity retention rate (i.e., the same deterioration
level), the internal resistance r becomes larger as the ambient
temperature decreases. On the other hand, the open circuit voltage
E of the secondary battery 14 is constant without being affected by
the ambient temperature. The terminal voltage V of the secondary
battery 14 becomes higher as the ambient temperature decreases.
Therefore, the voltage at which the distinctive point P appears
becomes higher as the ambient temperature decreases. The difference
between the set voltage for estimating the battery capacity X and
the voltage V at which the distinctive point P appears becomes
smaller as the ambient temperature decreases. Therefore, the period
T becomes shorter as the ambient temperature decreases.
[0131] (7) In the first embodiment, the "battery capacity" X of the
secondary battery 14 is described as an example of the "condition"
of the electric storage device, and the battery capacity X of the
secondary battery 14 is estimated based on the voltage V at which
the distinctive point P appears. The "condition" of the electric
storage device is not limited to the battery capacity X of the
secondary battery 14, but may be the "internal resistance" r of the
secondary battery 14. The battery capacity (deterioration level) X
of the secondary battery 14 is correlated with the internal
resistance r of the secondary battery 14, and thus the internal
resistance r of the secondary battery 14 is correlated with the
voltage V at which the distinctive point P appears. Therefore, the
internal resistance r of the secondary battery 14 can be estimated
based on the voltage V at which the distinctive point P appears.
Specifically, experiments may be conducted for measuring voltages V
of the secondary batteries 14 having different internal resistances
r (having the same initial capacity) at which the distinctive
points P appear. Then, correlation data that contains the voltages
V at which the distinctive points P appear in association with the
internal resistances r of the secondary batteries 14 (similar to
the data in FIG. 4) may be created. The internal resistance r of
the secondary battery 14 can be estimated by the voltage at which
the distinctive point P appears based on the correlation data. In
addition, correlation data that contains the periods T in
association with the internal resistances r of the secondary
battery 14 (similar to the data in FIG. 4) may be created. The
internal resistance r of the secondary battery 14 can be estimated
by the period T based on the correlation data.
[0132] (8) In the first embodiment, the second distinctive point P2
is detected based on the startup voltage Vo, but may be detected by
other methods based on other factors than the startup voltage Vo.
For example, the distinctive point P that is detected at a time
close to the time at which the secondary battery 14 reaches the set
voltage (4.1 V in this embodiment) may be detected as the
distinctive point, which is used for measuring the period. The
voltage at which the distinctive point P is detected may be
compared with the range of the voltage at which the second
distinctive point P2 appears to determine whether the distinctive
point P is the second distinctive point P2. It is preferable to
detect the distinctive point P by a plurality of methods to detect
the second distinctive point P2 with higher accuracy.
[0133] (9) In the first to fourth embodiments, the battery pack 60
is installed in an electric vehicle or a hybrid vehicle. However,
the application of the present technology is not limited to an
electric vehicle (EV) or a hybrid vehicle (HV). The present
technology may be applied to any apparatus or system in which an
electric storage device such as the secondary battery 14 is
installed. For example, the present technology may be applied to a
train or a plug-in electric hybrid vehicle (PHEV). In addition, the
present technology may be applied to an energy system having an
electric storage function such as a home energy management system
(HEMS). Other than the condition estimation device, the embodiments
described herein can be used in various applications including a
method of estimating a condition of an electric storage device such
as the secondary battery 14, a computer program for executing the
function of the device or the method, and a recording medium that
stores the computer program.
[0134] (10) In the fourth embodiment, the remaining capacity at
which the second distinctive point P2 appears is set as the fixed
value Z, and the fixed value Z is determined as the remaining
capacity of the secondary battery 14. However, as described with
reference to FIG. 19, the voltages V at which the second
distinctive points P2 appear in the secondary batteries 14 differ
from one another depending on the ambient temperature although the
secondary batteries 14 have the same battery capacity X. The
voltage V at which the second distinctive point P2 appears becomes
lower as the ambient temperature decreases. The same tendency is
applied to the remaining capacity at which the second distinctive
point P2 appears (during the discharge, the voltage V at which the
second distinctive point P2 appears becomes higher as the ambient
temperature decreases). Therefore, different pieces of the
correlation data that contains the remaining capacities of the
secondary batteries 14 at which the second distinctive points P2
appear in association with the ambient temperatures may be prepared
for different ambient temperatures.
[0135] (11) In the fourth embodiment, the fixed value Z is the
smallest one of the remaining capacities obtained in the above
experiments to have less risk of the lack of electricity. However,
the present technology is not limited thereto. The fixed value Z
may be the largest one of the remaining capacities obtained in the
above experiments or may be a mean value of the remaining
capacities.
[0136] (12) In the fourth embodiment, the ratio W is the smallest
one of the ratios obtained in the experiment to have less risk of
the lack of electricity. However, the present technology is not
limited thereto. The ratio W may be the largest one of the ratios
obtained in the experiment or a mean value of the ratios.
* * * * *